A typical data storage system includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute. Digital information, representing various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to an actuator and passed over the surface of the rapidly rotating disks.
The actuator typically includes a plurality of outwardly extending arms with one or more transducers being mounted resiliently or rigidly on the extreme end of the arms. The actuator arms are interleaved into and out of the stack of rotating disks, typically by means of a coil assembly mounted to the actuator. The coil assembly generally interacts with a permanent magnet structure, and the application of current to the coil in one polarity causes the actuator arms and transducers to shift in one direction, while current of the opposite polarity shifts the actuator arms and transducers in an opposite direction.
In a typical digital data storage system, digital data is stored in the form of magnetic transitions on a series of concentric, closely spaced tracks comprising the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors, with each sector comprising a number of information fields. One of the information fields is typically designated for storing data, while other fields contain sector identification and synchronization information, for example. Data is transferred to, and retrieved from, specified track and sector locations by the transducers being shifted from track to track, typically under the control of a controller. The transducer assembly typically includes a read element and a write element. Other transducer assembly configurations incorporate a single transducer element used to write data to the disks and read data from the disks.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the transducer assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals in the read element. The electrical signals correspond to transitions in the magnetic field.
Conventional data storage systems generally employ a closed-loop servo control system for accurately and rapidly positioning the actuator and read/write transducers to specified storage locations on the data storage disk. A servo writing procedure is typically implemented to initially record servo information on the surface of one or more of the data storage disks. A servo writer assembly is typically used by manufacturers of data storage systems to facilitate the transfer of servo data to one or more data storage disks during the manufacturing process. In accordance with one known servo information format, termed an embedded servo, servo information is written between the data storing sectors of each track. The servo data is thus embedded in the data storing tracks of the data storage disks, typically resulting in an alternating sequence of data and servo sectors comprising each track.
In accordance with another known servo information format employed in data storage systems, termed a dedicated servo, the servo writer records servo information typically on only one of the data storage disks comprising the disk stack, and often on only one of the surfaces of the dedicated servo disk. The servo information stored on the dedicated servo disk is used to maintain accurate positioning and alignment of the read/write transducers associated with each of the data storage disks. During normal data storage system operation, a servo transducer, generally mounted proximate the read/write transducers, or, alternatively, incorporated as part of the read element of the transducer, is typically employed to read the servo sector data for the purpose of locating specified track and data sector locations on the disk. It is noted that a servo sector typically contains a pattern of data, often termed a servo burst pattern, used to maintain optimum alignment of the read/write transducers over the centerline of a track when reading and writing data to specified data sectors on the track.
It is recognized by those skilled in the art that the performance of the spindle motor is critical to providing a high level of data storage system performance and reliability. Normal and accelerated wearing of the spindle motor assembly and, in particular, the spindle motor bearings, have been associated with a general degradation in data storage system performance. Reading and writing data to and from a data disk, for example, can be negatively affected by a failure mechanism, often referred to as non-repeatable runnout, that results from spindle motor bearing assembly damage. Non-repeatable spindle motor runnout is often induced by irregular or perturbed spindle motor and data storage disk rotation caused by excessively worn or damaged spindle motor bearings.
As the transducer is transferring data to or from a particular track, for example, such perturbations in the rotation of the data storage disk cause the transducer to deviate from its preferred centerline orientation over the track, often resulting in track misregistration and data transfer errors of varying severity. It is noted that detrimental perturbations in spindle motor rotation associated with spindle motor bearing assembly damage generally result in both radial and vertical displacement of the data storage disk in a random, non-repeatable manner. As such, the control algorithm employed in the servo control system typically cannot be modified to accommodate such random off-centerline tracking deviations.
Further, irregularities in the precision machined surfaces of the spindle motor bearings and deformations in the bearing race, for example, typically result in increased friction within the spindle bearing assembly and accelerated bearing assembly fatigue. Increased bearing friction has also been associated with the production of particulate contaminates that can adversely or catastrophically interfere with the operation of other data storage system components. Such undesirable changes in the spindle bearing assembly operating condition generally lead to a progressive degradation in spindle motor performance, increased consumption of spindle motor supply current to overcome additional mechanical friction, and, more significantly, a higher probability of temporary or permanent loss of data stored on one or more data storage disks mounted to the hub of the spindle motor.
It is generally considered highly desirable to detect changes in the performance of the spindle motor early in, and throughout, its service life in order to minimize the probability of intermittent and catastrophic failure of the data storage system. A number of elaborate and typically expensive predictive failure analysis methodologies have been developed in an attempt to detect the existence of failure modes associated with degradation in data storage system performance. Many of these prior art methodologies, for example, can be implemented only after installation of additional supporting electronic hardware and control circuitry into the data storage system, thus adding to the overall cost and complexity of the system. Moreover, such prior art failure analysis procedures often require disassembly of the data storage system housing, or require that a separate, external testing apparatus be coupled to the system in order to perform one or more diagnostic procedures.
A trend has developed in the data storage system manufacturing community to miniaturize the chassis or housing of a data storage system to a size suitable for incorporation into miniature personal computers, such as lap-top and pocket-sized computers, for example. Various industry standards have emerged that specify the external housing dimensions of small and very small form factor data storage systems. One such recognized family of industry standards is the PCMCIA (Personal Computer Memory Card Industry Association) family of standards, which specifies both the dimensions for the data storage system housing and the protocol for communicating control and data signals between the data storage system and a host computer system coupled thereto. Recently, four families or types of PCMCIA device specifications have emerged. By way of example, a Type-I PCMCIA data storage system must be fully contained within a housing having a maximum height dimension of 3.3 millimeters (mm). By way of further example, a Type-II PCMCIA device housing must not exceed a maximum height of 5.0 mm in accordance with the PCMCIA specification. A maximum height of 10.5 mm is specified for the housing of Type-III PCMCIA devices, and Type-IV devices are characterized as having a maximum housing height dimension in excess of 10.5 mm.
It is anticipated that the industry trend of continued miniaturization of data storage systems will eventually result in the production of systems complying with the Type-II PCMCIA specification. Such Type-II PCMCIA data storage systems will likely have external housing dimensions of approximately 54 mm.times.86 mm.times.5 mm, and include a data storage disk having a diameter of approximately 45 mm and a width dimension similar to that of a standard credit card. In small and very small form factor data storage systems, which, in general, are particularly susceptible to spindle motor bearing fatigue, the relatively compact packaging configuration of such miniaturized systems often preclude employment of a predictive failure analysis scheme that requires installation of additional system components.
There exists in the data storage system manufacturing industry a keenly felt need to provide an in-situ spindle motor predictive failure analysis tool that detects degradation in spindle motor performance during the service life of the spindle motor. There exists a further need to provide such a detection tool that requires little or no modification to the existing configuration of a data storage system, and only minimally impacts the standard operation of the system. The present invention fulfills these and other needs.